Electron beam welding systems employing a plasma cathode

Abstract

In an embodiment, a system is provided that includes an electron gun, a focusing system, and a housing. The electron gun can include a cold cathode electron source and an extraction electrode. The focusing system can be configured to focus a beam of electrons extracted from the electron gun to a focal region. The housing can include the electron gun and extend along a housing axis in the direction of the electron beam. The cold cathode source is configured to emit electrons at a first operating pressure that is higher than a second operating pressure at the focal region of the electron beam.

1 . A system, comprising:
 an electron gun including a cold cathode electron source and an extraction electrode;   a focusing system configured to focus a beam of electrons extracted from the electron gun to a focal region; and   a housing including the electron gun and extend along a housing axis in the direction of the electron beam;   wherein the cold cathode source is configured to emit electrons at a first operating pressure that is higher than a second operating pressure at the focal region of the electron beam.   
     
     
         2 . The system of  claim 1 , wherein the cold cathode electron source is a plasma cathode includes:
 a plasma cathode chamber;   a first plasma electrode mounted to a first wall of the plasma cathode chamber; and   a second plasma electrode mounted to a second wall of the plasma cathode chamber, opposite the first wall;   wherein an axis of the plasma cathode chamber extends in the direction between the first and second plasma electrodes.   
     
     
         3 . The system of  claim 2 , wherein the plasma cathode is configured to generate a plasma having an electron temperature less than about 200° C. 
     
     
         4 . The system of  claim 2 , wherein the plasma cathode chamber axis is approximately aligned with the housing axis. 
     
     
         5 . The system of  claim 2 , wherein the plasma cathode chamber axis is approximately perpendicular to the housing axis. 
     
     
         6 . The system of  claim 1 , wherein the first operating pressure within the range from about 50 millitorr to about 500 millitorr. 
     
     
         7 . The system of  claim 6 , wherein the second operating pressure is within the range from about 1 millitorr to about 50 millitorr. 
     
     
         8 . The system of  claim 1 , wherein the housing includes the electron gun and a welding chamber enclosing the focal region. 
     
     
         9 . The system of  claim 1 , wherein the housing further comprises a differentially pumped snorkel extending between a first end coupled to the electron gun and a second free end, wherein the snorkel is configured to provide a selected pressure gradient between the first end and the second end, and wherein the focal region is approximately positioned at the second free end. 
     
     
         10 . The system of  claim 9 , wherein the snorkel comprises a plurality of vacuum enclosures, each in fluid communication with a respective vacuum pump. 
     
     
         11 . A method, comprising:
 generating, by an electron gun including a cold cathode source and an extraction electrode, electrons at a first pressure;   extracting, by the extraction electrode, a electrons emitted from the cold cathode source;   focusing a beam of the extracted electrons to a focal region along an axis of a housing containing the electron gun; and   receiving, incident upon a surface of the work piece, the focal region of the electron beam, wherein a second pressure at the work piece is less than the first pressure.   
     
     
         12 . The method of  claim 11 , wherein generating the electrons comprises:
 receiving a flow of gas within a plasma cathode chamber of the electron gun; and   generating an electric field between a first plasma electrode mounted to a first wall of the plasma cathode chamber and a second plasma electrode mounted to a second wall of the plasma cathode chamber, opposite the first wall, wherein the electric field is configured to form a plasma from the gas;   wherein an axis of the plasma cathode chamber extends in the direction between the first and second plasma electrodes.   
     
     
         13 . The method of  claim 11 , wherein the generated plasma has an electron temperature less than about 200° C. 
     
     
         14 . The method of  claim 12 , wherein the plasma cathode chamber axis is approximately aligned with the housing axis. 
     
     
         15 . The method of  claim 12 , wherein the plasma cathode chamber axis is approximately perpendicular to the housing axis. 
     
     
         16 . The method of  claim 12 , wherein the first pressure is within the range from about 50 millitorr to about 500 millitorr. 
     
     
         17 . The method of  claim 16 , wherein the second pressure is within the range from about 1 millitorr to about 50 millitorr. 
     
     
         18 . The method of  claim 11 , further comprising enclosing the work piece within a welding chamber, wherein the welding chamber is in fluid communication with the electron gun. 
     
     
         19 . The method of  claim 11 , further comprising:
 forming a vacuum seal between a surface of the work piece and a free end of a snorkel, the snorkel extending from the free end to the electron gun; and   establishing a selected pressure gradient along the length of the snorkel between the electron gun and the free end.   
     
     
         20 . The method of  claim 19 , wherein establishing the selected pressure gradient comprises applying vacuum pressure of different levels to respective vacuum enclosures of the snorkel.